Communication devices such as Mobile Stations (MS) are also known as e.g. mobile terminals, wireless terminals and/or user equipment. A mobile station is enabled to communicate wirelessly in a cellular communications network, wireless communications system, or radio communications system, sometimes also referred to as a cellular radio system, cellular network or radio access network (RAN), to mention some examples. The communication may be performed e.g. between two mobile stations and between a mobile station and a regular telephone.
The mobile station may further be referred to as a mobile telephone, cellular telephone, laptop, Personal Digital Assistant (PDA), tablet computer, surf plate, just to mention some further examples. The mobile station in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another mobile station or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by a Base Station (BS), which sometimes may be referred to as Radio Base Station (RBS), Base Transceiver Station (BTS), just to mention some examples. The base stations may be of different classes based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the mobile station within range of the base stations.
Several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Base Station Controller (BSC) in GSM. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Special Mobile). The BSC may supervise and coordinate various activities of the plural base stations connected thereto.
When nothing else is indicated, the expression downlink (DL) generally refers to transmission from the base station to the mobile station and the expression uplink (UL) generally refers to transmission in the opposite direction i.e. from the mobile station to the base station.
In General Packet Radio Service (GPRS), Enhanced GPRS (EGPRS) and EGPRS phase 2 (EGPRS2), the packet data bearers of the GSM radio access network, data connections for several users are multiplexed onto shared channels, aka Packet Data Shared Channels (PDCHs). A PDCH is a physical channel using one timeslot in each Time Division Multiple Access (TDMA) frame on the radio interface. Four consecutive timeslots on the PDCH (sent in four consecutive TDMA frames) form a radio block. The radio block is the smallest entity that can be used for transmission and reception of data for a GPRS/EGPRS/EGPRS2. In the downlink, each radio block is addressed to a particular MS. Similarly, in uplink a particular mobile station is allowed to transmit during a given radio block. The duration of a radio block is approximately 20 ms.
The TDMA frame of GPRS/EGPRS/EGPRS2 has eight timeslots. Therefore, up to eight PDCHs can be transmitted in parallel on one GSM carrier. Radio blocks, one for each PDCH, that is, one for each of the eight TDMA frame timeslots, numbered 0-7, are schematically illustrated in FIG. 1. Units along a horizontal axis in FIG. 1 is thus TDMA frame timeslot and unit along a vertical axis is thus radio block periods. Mobile stations with multislot capability may transmit and/or receive several PDCHs in parallel.
The multiplexing of mobile stations on the uplink is controlled by the network as follows. In each downlink radio block, an mobile station address field is transmitted. This is known as the Uplink State Flag (USF). For a given PDCH, each MS has been given a unique USF value. When that USF value is received by the mobile station on a downlink PDCH it has been assigned, it is allowed to transmit during the next radio block on the corresponding uplink PDCH. If USF granularity is used (signaled to the MS when it was assigned the PDCH), the mobile station is also allowed to transmit during the three subsequent radio blocks on the same PDCH, i.e., in total during four radio blocks.
This multiplexing method is referred to as Dynamic Allocation (DA) and is illustrated by examples in FIG. 2 and FIG. 3.
For example, in FIG. 2 mobile station MS X has been assigned USF value 1. This USF value is transmitted on downlink timeslot 2 during radio block period N and allows MS X to transmit a radio block on the corresponding uplink timeslot during next radio block period N+1. Units along horizontal and vertical axis in FIG. 2 corresponds to what was shown and discussed above in connection with FIG. 1. Mobile station MS Y has been assigned USF value 2. This USF value is transmitted on timeslot 3 and allows MS Y to transmit a radio block on uplink timeslot 3. In FIG. 3 MS X has been assigned USF value 1. This USF value is transmitted on downlink timeslot 2 and allows MS X to transmit four consecutive radio blocks on the corresponding uplink timeslot. MS Y has been assigned USF value 2. This USF value is transmitted on timeslot 3 and allows MS Y to transmit four consecutive radio blocks on uplink timeslot 3.
Sometimes it is necessary to use an extension to this multiplexing method, called Extended Dynamic Allocation (EDA). This is similar to DA, with the difference that when an MS receives its assigned USF value on a given PDCH, it is allowed to transmit not only on the corresponding uplink PDCH, but also on all uplink PDCHs it has been assigned with higher timeslot numbers in the TDMA frame. USF granularity may be used also together with EDA. For example, in FIG. 4 mobile station MS X is assigned USF value 1 and uplink timeslots 2, 3 and 4. This USF value is transmitted on downlink timeslot 2 and allows MS X to transmit a radio block on each of uplink timeslots 2, 3 and 4.
The existing solutions are described in further detail in 3GPP TS 44.060 “RLC/MAC protocol”, where multiplexing principles are described in clause 5.2 and DA and EDA in clause 8.1.1, and in 3GPP TS 45.002 “Multiplexing and multiple access on the radio path”, where clause 6.3.2.2.1 describes DA and EDA to some extent.
The USF is a three bit field and hence it can address eight unique mobile stations per PDCH.
With an increasing amount of users, devices to be provided with internet access and in order to realize the vision of “50 billion” users, it is desirable or even necessary to be able to multiplex many mobile stations on each PDCH. However, since the USF can only address eight unique mobile stations, no more than eight mobile stations can share one uplink PDCH.